In Long Term Evolution (LTE), the scheduler is placed in the eNodeB and the Medium Access Control (MAC) layer. The scheduler assigns radio resources, also called Resource Blocks (RB). The user equipments find out where to listen or where to send by listening for downlink assignments and uplink grants on the Physical Downlink Control Channel (PDCCH). Also, information concerning which transport format to use is comprised within the assignment and grant, respectively.
The radio downlink is the transmission path from a base station, e.g. an eNodeB to a terminal, or a User Equipment (UE) as the terminal also may be referred to as. The uplink is the inverse of a downlink, i.e. the transmission path from the terminal to the base station.
However, as the eNodeB schedules uplink transmissions, while the buffers are located in the terminal or user equipment (UE), the terminal has to notify the eNodeB that it has data that it would like to transmit. If notification is not possible, the eNodeB has to schedule the user equipment blindly without knowledge as to whether there is data in the buffer of the UE. The terminal supplies the eNodeB with information about the data in its buffers using two mechanisms; a 1-bit Scheduling Request (SR) or Buffer Status Reports (BSR). Scheduling requests are transmitted on a control channel such as e.g. Physical Uplink Control Channel (PUCCH) or Random Access Channel (RACH). This process is illustrated in FIG. 1, which depicts prior art uplink scheduling. Buffer status reports are however transmitted on a data channel such as Physical Uplink Shared Channel (PUSCH) mostly together with user data.
If the terminal has a valid PUCCH resource for scheduling request configured in any Transmission Time Interval (TTI), it sends a one bit scheduling request when the timing is right, that is, when the PUCCH resources are available. Otherwise it initiates a random access procedure and cancels all pending scheduling requests.
The terminal is only allowed to use the PUCCH for the SR at predefined points in time determined by the Dedicated Scheduling Request (D-SR) interval. The delay between the actual generation time of a data packet such as e.g. a Voice over the Internet Protocol (VoIP) packet and the sending of the D-SR can thus become as large as the D-SR interval. It is to be noticed that VoIP is here used merely as a clarifying example of a service; the present invention is by no means limited to be used only for VoIP, but may bring advantages for any kind of service.
In the present context, the generation time of data packets or data frames, i e frames of data, is defined as the actual time when the data was put in the transmit buffer at the terminal. Scheduling request arrival time is defined as the time when the eNodeB receives a scheduling request. Similarly, data arrival time may be defined as the time when the eNodeB receives a data packet or data frame transmitted by the UE.
When using service aware buffer estimation such as e.g. VoIP aware buffer estimation, the generation time is valuable to obtain the shortest possible delay for the data packet or data frame.
In VoIP, the buffer estimation algorithm moves between two states, Silence Insertion Descriptor (SID) and TALK and a state change should preferably occur when the codec switches between the corresponding states. The TALK state is a proactive buffer estimation state which guesses when the next voice frame, i e frame of voice data, or data packet comprising voice data will arrive and which size it will have, while the SID state is a passive state that expects Scheduling Requests when data has arrived for a user.
As voice frames arrive every 20 ms to the terminal buffer using for instance Adaptive Multi Rate (AMR), the better the algorithm knows the generation time, the more exact it will predict the buffer size. This way the delay of the voice frame can be minimized.
The larger the D-SR interval is, the larger the difference between the generation time of the VoIP packet and the arrival time when the eNodeB notes the data arrival. This makes it harder to accurately predict the buffer state or buffer size and schedule delay-sensitive services, increasing the need for explicit signalling and decreasing the efficiency of the uplink assignments.
The VoIP aware buffer estimator uses the arrival time of the D-SR, deducted by the processing time, as the VoIP packet generation time. This time can be very different from the actual VoIP packet generation time. Furthermore, the eNodeB scheduler does not have correct packet delay information and may schedule the VoIP packet too late, especially in scenarios where the required VoIP delay is relatively short. In addition, the user equipment may need to be active and monitor PDCCH during the time from packet generation time until scheduling event. Long delay between these events consumes battery of the user equipment.
It is to be noted that the scheduling request is a scarce resource and thus the D-SR interval can be relatively long compared to the time between generation of voice packets at the terminal.
LTE provides a mechanism referred to as Discontinuous Reception (DRX) which intends to reduce the user equipments' battery consumption by allowing them to disable their receiver chain under certain conditions. According to the current LTE specification, a user equipment must leave DRX, i.e. enable the receiver chain and monitor PDCCH, upon a scheduling request trigger which is typically before the scheduling request is sent. For certain services such as VoIP this requirement bears the risk that the user equipment can hardly ever enter DRX. This is due to the fact that the eNodeB has no means to determine the time when the data frame, e.g. VoIP packet, entered the buffer and triggered the scheduling request.
US 2008/0119181 A1 concerns a radio base station, a radio communication terminal, and a radio communication system that can utilize broadband resources even if many packets of different sizes and different QoS requirements are mixed when sent and received. When a data transmission request is sent from a radio terminal to a base station, at least one of a data transmission duration time, a transmission data transmission interval, and an expiration time is included in the data transmission request. The base station receives data transmission requests from multiple radio terminals, schedules the data transmission requests from multiple radio terminals, assigns bandwidths to the multiple radio terminals based on the duration time, transmission interval, and expiration time included in each of the data transmission requests and continues the assignment of bandwidths to the radio terminals during the duration time based on the received duration time.
WO 2007/024120 A1 relates to a resource request and a packet scheduling method for uplink traffic in a mobile communication system. For efficient scheduling of the uplink traffic, a base station and user equipment determines a scheduling method according to characteristics of the traffic when performing negotiation therebetween. The traffic may be classified into traffic that generating a fixed-size packet in a periodical time interval, traffic that generates a variable-size packet in a periodic time interval, and traffic that generates a variable-size packet in a random time interval, and then scheduled.